The present invention relates to a method for producing a liquid crystal display device and to a liquid crystal display device.
Liquid crystal display devices are widely used in personal computers, portable electronic apparatus and the like. Generally, a liquid crystal display device comprises, as shown in FIG. 36, a liquid crystal layer 7 sandwiched between two substrates 1, on which color filters 4, a black matrix 5, transparent electrodes 3, an alignment layer 9 and so on are formed.
A TFT (thin film transistor) type liquid display device, as shown in FIG. 37, comprises a liquid crystal layer 7 sandwiched between a substrate 1a, which comprises a glass substrate 1 with transparent electrodes 3, color filters 4, a conductive black matrix 5, an overcoat layer 6, an alignment layer 9 and so on formed thereon, and a substrate 1b, which comprises a glass substrate 1 with transparent electrodes 3 each comprising a source electrode 14a, a drain electrode 14 and so on, insulating films 23, semiconductor films 16, gate electrodes 13, an alignment layer 9 and so on formed thereon.
In these liquid crystal display devices, it is spacers that regulate the distance between the two substrates and maintain the thickness of the liquid crystal layer at an appropriate level.
According to the prior art methods of liquid crystal display device production, spacers are sprayed and dispersed randomly but uniformly over the substrate on which pixel electrodes are formed. Therefore, as shown in FIG. 36 and FIG. 37, spacers are disposed also at the sites of some pixel electrodes, namely at some display sites of the liquid crystal display device. Spacers are generally made of a synthetic resin, glass or a like material and, when a spacer is disposed on a pixel electrode, its depolarizing action causes light leakage at the spacer site. Further, the liquid crystal alignment is disturbed on the spacer surface, causing a bright defect, hence the contrast and color tone are decreased and the display quality is deteriorated.
To solve such problems as mentioned above, spacers should be disposed only in spaces among neighboring electrodes, which are not display sites, namely only at sites covered by the black matrix, which is a light shield layer. The black matrix is provided for the purpose of improving the contrast of display of a liquid crystal display device or, in the case of a TFT type liquid crystal display device, for the purpose of preventing error operation of elements due to external light.
A technology of disposing spacers at sites corresponding to the black matrix, namely at sites other than display pixel sites, of a TFT type liquid crystal display device is disclosed in Japanese Kokai Publication Hei-04-256925 which comprises maintaining the gate electrode and drain electrode at the same electric potential in the step of spraying spacers. Further, Japanese Kokai Publication Hei-05-53121 discloses a method comprising applying a voltage to the circuit electrodes in the step of spacer spraying, while Japanese Kokai Publication Hei-05-61052 discloses a method comprising applying a positive voltage to the circuit electrodes and charging spacers negatively and spraying them by the dry method.
The inventions described in the references cited above use a substrate having thin film transistors (TFTs) formed thereon and control the spacer disposition by applying a voltage to the circuits of these thin film transistors.
However, they have a problem. Namely, application of a voltage to the substrate having thin film transistors (TFTS) formed thereon, for the purpose of controlling the spacer disposition may lead to destruction of elements by that voltage, hence to failure to function as a liquid crystal display device.
There is another problem. Namely, such technologies as mentioned above cannot be employed in STN type liquid display devices since the sites corresponding to the black matrix are spaces among transparent electrodes.
On the other hand, as a technology of disposing spacers in spaces between stripe-form transparent electrodes constituted by disposing a plurality of linear transparent electrodes in parallel on a substrate, as in STN type liquid crystal display devices, there is disclosed, in Japanese Kokai Publication Hei-04-204417, a method of producing liquid crystal display devices which comprises charging spacers either positively or negatively and applying a voltage of the same polarity to the linear transparent electrodes on the substrate in the step of spacer spraying.
This production method is intended to dispose spacers in interelectrode spaces by applying a voltage of the same polarity as the spacer charge polarity to the linear transparent electrodes to thereby cause spacer-electrode repulsion. However, mere application of a voltage of the same polarity as the spacer charge to the linear transparent electrodes cannot attain a sufficient reduction in electric potential between the transparent electrodes but leads to such a state as shown in FIG. 9. Thus, any electric field suited for spacer disposition is not formed, hence the precision of spacer disposition is very poor. It is therefore impossible to improve the contrast of the product liquid crystal display device to a satisfactory extent.
Accordingly, it is an object of the present invention to provide a method for producing a liquid display device by which the above problems are solved and which enables spacer disposition in interelectrode spaces where there is no electrode, namely at black matrix sites, in STN type and TFT type liquid crystal display devices and further enables even spacer disposition to attain a uniform cell thickness all over the substrate to thereby produce liquid crystal display devices of high contrast and high display uniformity stably and in good yields, with a reduced spray step tact time, as well as liquid crystal display devices produced by such method.
In a first aspect, the present invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, disposing the substrate in close contact with an earthed conductive stage having a volume resistance of not more than 1010 xcexa9cm,
and a voltage of 200 V to 5 kV having the same polarity as the spacer charge polarity is applied to the transparent electrodes.
In a second aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes, a conductive black matrix and an overcoat layer and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, a voltage (V1) is applied to the conductive black matrix and a voltage (V2) to the transparent electrodes,
both the voltages V1 and V2 being positive ones and satisfying the relation V1 less than V2 when the spacer charge polarity is positive,
or both V1 and V2 being negative voltages and satisfying the relation V1 greater than V2 when the spacer charge polarity is negative.
In a third aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes, an alignment layer and one or more display areas and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, the substrate is disposesd in close contact with an earthed conductive stage having a size smaller than the substrate size to thereby allow the peripheral edge portions thereof to be apart from the conductive stage,
and a voltage of the same polarity as the spacer charge polarity is applied to the transparent electrodes on the substrate.
In a fourth aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and an alignment layer and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
and comprising the step of removing water from the substrate onto which spacers are to be sprayed, and the step of bringing the substrate into close contact with an earthed conductive stage and then spraying spacers while applying a voltage of the same polarity as the spacer charge polarity to the transparent electrodes on the substrate.
In a fifth aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and an alignment layer and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
and comprising the step of disposing the substrate into close contact with an earthed conductive stage and spraying spacers while applying a voltage of the same polarity as the spacer charge polarity to the transparent electrodes on the substrate,
the substrate before and during spacer spraying showing characteristics such that, when a voltage of 1 kV is applied to the transparent electrodes on the substrate, the current flowing between the transparent electrodes on the substrate and the conductive stage is not more than 10xe2x88x926 A.
In a sixth aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and an alignment layer and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, the substrate is disposed into close contact with an earthed conductive stage,
a voltage of the same polarity as the spacer charge polarity is applied to the transparent electrodes on the substrate,
then the terminals of the voltage application apparatus are disconnected from the transparent electrodes,
and spacer spraying is carried out while the electric charge remains on the substrate.
In a seventh aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrode and an alignment layer and a second substrate to be disposed opposingly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, the substrate is disposed into close contact with an earthed conductive stage,
a voltage of the same polarity as the spacer charge polarity is applied to the transparent electrodes on the substrate while maintaining that state of voltage application for a certain period of time
and then spacer spraying is carried out while maintaining that state of voltage application.
In an eighth aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto a first substrate comprising at least pattern-forming transparent electrode, a conductive black matrix, an overcoat layer and an alignment layer,
and filling a liquid crystal into the space between the first substrate and a second substrate comprising thin film transistors formed thereon which is to be disposed opposingly above the first substrate,
wherein the first substrate has transparent electrode-free etched regions formed within the transparent electrodes over and within the expanse of the corresponding conductive black matrix areas,
and, in spraying positively or negatively charged spacers onto the first substrate, a voltage (V1) is applied to the conductive black matrix and a voltage (V2) to the transparent electrodes,
both the voltages V1 and V2 being positive ones and satisfying the relation V1 less than V2, when the spacer charge polarity is positive,
or both V1 and V2 being negative voltages and satisfying the relation V1 greater than V2, when the spacer charge polarity is negative.
In a ninth aspect, the invention provides a method for producing a liquid crystal display device
comprising spraying spacers onto a first substrate comprising at least pattern-forming transparent electrodes, a black matrix, an overcoat layer and an alignment layer,
and filling a liquid crystal into the space between the first substrate and a second substrate comprising thin film transistors formed thereon which is to be disposed opposingly above the first substrate,
wherein the first substrate has transparent electrode-free etched regions formed within the transparent electrodes over and within the expanse of the corresponding conductive black matrix areas,
and, in spraying positively or negatively charged spacers onto the first substrate, the first substrate is disposed into close contact with an earthed conductive stage having a volume resistance of not more than 1010 xcexa9cm
and a voltage of 200 V to 5 kV having the same polarity as the spacer charge polarity is applied to the transparent electrodes.
In a tenth aspect, the invention provides a method for producing a liquid crystal display device comprising spraying spacers onto a first substrate comprising at least pattern-forming transparent electrodes,
and filling a liquid crystal into the space between the first substrate and a second substrate comprising thin film transistors formed thereon which is to be disposed opposingly above the first substrate,
wherein the first substrate has isolated, electrically floating, transparent electrodes not connected with the surrounding transparent electrodes but formed within the transparent electrodes within the expanse of the corresponding black matrix areas as formed on the first or second substrate,
and, in spraying positively or negatively charged spacers onto the first substrate, the first substrate is disposed in close contact with an earthed conductive stage having a volume resistance of not more than 1010 xcexa9cm
and a voltage of the same polarity as the spacer charge polarity is applied to the transparent electrodes other than the isolated transparent electrodes on the first substrate.
In an eleventh aspect, the invention provides a method for producing a liquid crystal display device according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth or tenth aspect of the invention,
wherein spacers are charged positively or negatively by being sprayed through a pipeline made of a resin or a metal using a gas as a medium.
In a twelfth aspect, the invention provides a method for producing a liquid crystal display device according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth or eleventh aspect of the invention,
wherein spacers are fixed on the substrate surface by heating.
In a thirteenth aspect, the invention provides liquid crystal display devices produced by the method for producing a liquid crystal display device according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh or twelfth aspect of the invention.